We will continue our research on the mechanism by which reovirions acquire a unique set of 10 double-stranded (DS) genome RNA segments during morphogenesis. Our studies have clearly established that the assembly of DS genome RNA takes place at the level of single-stranded (SS) RNA. More specifically 10 segments of SS RNA and viral polypeptides associate to form subviral particles and DS RNA is synthesized within these particles. We are currenty isolating and characterizing protein-RNA complexes from infected cells to determine the recognition mechanism between SS RNA segments and viral polypeptides. We will also continue our studies on the structure of reovirus cores. We have demonstrated that the twelve surface spikes consist of polypeptide lambda 2. Next we wish to determine how the remaining two polypetides are oriented in the cores in relationship to the genome RNA.